The gene expression of beta globulin mRNAs of mouse erythroleukemia cells is analyzed in variant clones able or unable to synthesize hemoglobin in the presence of nonphysiological inducers of differentiated functions. Processing of the beta major and beta minor globin pre-mRNAs has been compared after dimethylsulfoxide or hemin treatment using Northern blots or S1 nuclease mapping.Two internal splice sites were detected during the processing of the large intervening sequence of beta major pre-mRNA, but not of the beta minor pre-mRNA. A model of processing of the mouse globin pre-mRNA is proposed. The role of the transferrin receptor in controlling the expression of the globin genes also is being investigated.